In recent years, while environments for taking advantage of the Internet or the like have been prepared, measurement systems including one for remote electric-power meter reading are being developed. Conventionally, to measure electric power, use has been made of the integrating wattmeter which converts power consumption to the number of revolutions of the disk for integration operation. Recently, the integrating wattmeter has been additionally provided with a sensor for detecting revolutions, an electric current meter (CT), or a potentiometer (PT) so as to perform multiplication computation with an electronic circuit or a microprocessor, thereby measuring the power. The integrating wattmeter has a complicated device structure, which is not only large but also expensive, and cannot be digitally controlled because the power is measured mechanically. Furthermore, in combination of these, extra energy may be consumed.
In this context, it is desired to develop a power meter which is capable of measuring power consumption as the amount of electric power as it is and which can be reduced in size and integrated.
On the other hand, in recent years, not only electrical devices for business use but also household electrical devices have increasingly incorporated high-frequency circuits, causing various adverse effects to occur due to the occurrence of harmonic currents. For example, in an area where cutting of the leakage of harmonic currents is loosely regulated, the leakage of harmonic currents has affected a surrounding household electrical device, e.g., causing the device to be on fire. Thus, there has arisen a social need for a sensor and a power measuring apparatus which can measure the occurrence of harmonic currents in a simplified manner.
As a substitute for the integrating wattmeter, for example, suggested were a power measuring apparatus and a magnetic field sensor therefor, which are capable of taking advantage of the magnetoresistance effect of the magnetic thin film so as to measure power consumption as the amount of electric power as it is (Non-Patent Literature 1). The power measuring apparatus and the magnetic field sensor are configured to employ a magnetic thin film (arranged on a substrate) disposed in parallel to a primary conductor through which an alternating current flows, allow a primary voltage to be applied to both the ends of the magnetic thin film via a resistor, and take the output on both the ends of the magnetic thin film. For example, this power measuring apparatus takes power IV from the amplitude value of the second harmonic component.
This power measuring apparatus or the like is configured to take a signal component proportional to power by focusing attention on the fact that linear characteristics can be obtained without a bias magnetic field by taking advantage of a planar hall effect (PHE) or a phenomenon that in a ferromagnet of magnetic thin film, the electrical resistance value of the magnetic substance varies depending on the angle formed between the current and the magnetization (this power measuring apparatus is referred to as “the planar hole type power measuring apparatus” or “the PHE type power measuring apparatus”).
Note that the magnetic field sensor employed here is an element for converting a change in an external magnetic field into an electrical signal, the element being configured such that a magnetic thin film such as a ferromagnetic thin film or a semiconductor thin film is patterned to flow current through the patterned magnetic thin film and the change in the external magnetic field is then converted as a change in voltage into the electrical signal.
However, the PHE type power measuring apparatus has to take the voltage output, to be detected across the magnetic thin film, in a direction orthogonal to the load current through a primary conductor. That is, the voltage has to be outputted on both the ends of the magnetic thin film in the width direction thereof. Thus, the PHE type power measuring apparatus needs to have a magnetic thin film increased in width to some extent, and thus cannot use a magnetic thin film reduced in width (which means here, e.g., a straight line shape or a rectangular shape that is thinner in the longitudinal direction). Furthermore, the PHE type power measuring apparatus has a geometric restriction that the magnetic thin film has to be formed of a bridge circuit. These mean that the PHE type power measuring apparatus can be installed with difficulty on a special line, such as the microstrip line or the coplanar line, which is employed in high-frequency circuits.
As other power measuring apparatuses for high-frequency use, a bolometer or precision measuring instrument may also available. However, such an instrument has a large complicated structure and is very expensive, so that the instrument cannot be used for power measurement or detection in each device or each facility.